It is well known that colorectal cancer and large polyps bleed into the stool. Use of guaiacum for the detection of blood was described in “The Scarlet Letter” by Sherlock Holmes as being sensitive but unreliable. The problem has been that guaiacum detects oxidizing agents of which blood is only one, and red meat and other oxidizing agents also can test positive.
A typical form of fecal occult blood testing known as Hemoccult II® utilizes a guaiac-treated test sheet upon which a specimen of fecal material is smeared. A developing solution is applied to the opposite side of the sheet yielding a blue color, which suggests that blood may be present in the fecal specimen. The drawback of this approach is that a high percentage of false positives is obtained from patients who in fact do not have a cancer or polyp. A false positive result in the test often results in expensive testing of patients who in fact have simply consumed a lot of meat just prior to the test.
One approach to overcome the high incidence of false positives has been to make the test paper sensitive enough to detect up to 2% of blood but not sensitive enough to produce too many false positives. A disadvantage of this compromise approach is that because of the reduced sensitivity, a number of cancers and polyps are not detected.
In an effort to increase sensitivity, the Hemoccult® SENSA system was devised (which results in detecting as little as 1000 micrograms of blood per ml of stool). However, this system results in a higher incidence of false positives requiring unnecessary invasive tests.
Alternative approaches to cutting down on false positives have involved placing patients on specific diets designed to restrict intake of animal proteins and other sources of false positives. Despite these efforts, large numbers of false positives still occur. One reason for this is the very long time it can take for food to pass through the bowel in certain patients.
A specific test for human hemoglobin has been devised. This test—the HemeSelect® test (now called Immudia-sp®)—theoretically registers only human hemoglobin and not animal blood from meat or other agents and therefore theoretically does not require the patient to be on a special diet. Another possible advantage is that human blood from the upper gastrointestinal tract may be digested by the time it reaches the stool and the only human blood detected would be that from the distal bowel. A serious drawback of the Immudia-sp® test is that it is expensive for a screening test and requires specially trained individuals to perform and read the test.
Devices and method for screening fecal occult blood specimens are described and claimed in U.S. Pat. Nos. 5,747,344 and 5,948,687. The entire disclosures of those two patents are herein incorporated by reference.
In recent years there have been significant advances in DNA/RNA testing of fecal matter. Present tests are very expensive often costing hundreds of dollars, and involve a whole stool specimen rather than a sample.
A need continues to exist for an inexpensive and easy-to-use fecal test which has a minimal incidence of false positives and can be readily used in a doctor's office. The invention of the present application seeks to meet that need.